1. Field of the Invention
The present invention relates to an automotive alternator which is to be mounted on a vehicle, and driven by an internal combustion engine to supply electric power to loads and charge a battery.
2. Description of the Related Art
FIG. 12 is a section view showing the configuration of a usual conventional automotive alternator, and FIG. 13 is an output characteristic diagram of the automotive alternator. Referring to FIG. 12, 1 denotes a stator core which is formed into a cylindrical shape, and which has a poly-phase stator winding 2, 3 and 4 denote front and rear brackets which hold the stator core 1, 5 denotes a claw-pole type rotor core which is disposed within the inner diameter of the stator core 1 with forming an air gap therebetween, which has a field winding 6, and which is fixed to a rotation shaft 7; 8a and 8b denote bearings which are disposed respectively on the front and rear brackets 3 and 4 to rotatably support the rotation shaft 7, 9 denotes a pulley which is disposed on one end of the rotation shaft 7 on the side of the front bracket 3, and which is driven by an internal combustion engine (not shown), 10 denotes a slip ring which is fixed to the rotation shaft 7 to supply a field current to the field winding 6, and 11 denotes a brush holder which is attached to the rear bracket 4, and which has brushes 12 that are in sliding contact with the slip ring 10.
In the thus configured conventional automotive alternator, the field current is supplied to the field winding 6 via the brushes 12 and the slip ring 10, and the pulley 9 is driven by the internal combustion engine which is not shown. Then, AC power is generated in the poly-phase stator winding 2. The AC power is rectified by a full-wave rectifier which is incorporated into the alternator, and which is not shown, and then used for charging a battery mounted on a vehicle and supplied to loads. A voltage control device which is not shown is incorporated into the alternator. The voltage control device turns on and off the field current to hold the output voltage to a predetermined value. The alternator has characteristics in which, in the case where the terminal voltage is held to the predetermined value, for example, 14 V, as shown in FIG. 13, the output voltage rises when the generated voltage exceeds a predetermined voltage, and is increased as the rotational speed is made higher, to be saturated in the high speed range.
On the other hand, such an automotive alternator is requested to have output characteristics in which, even in the low speed range of an internal combustion engine, i.e., the idling range, the output is sufficient for supplying electric power to loads and charging a battery. In order to increase the output current in such a low speed range, it may be first contemplated to increase the size, particularly, the outer diameter of the alternator, or the pulley ratio with respect to the engine so as to make the rotational speed higher. However, an automotive alternator which is to be mounted in an engine compartment of a vehicle must be miniaturized and lightened. Therefore, it is very difficult to increase the size. In the case where the alternator is driven by means of a poly-V belt or the like, for example, the increase of the pulley ratio causes belt slip. In order to suppress such belt slip, the diameter of a pulley on the side of the crankshaft of the engine must be increased. In accordance with this increase, also the diameters of pulleys for various belt-driven auxiliary devices must be increased, thereby causing the internal combustion engine to be enlarged.
The invention has been conducted in order to solve this problem. It is an object of the invention to provide an automotive alternator in which the output current in, particularly, the low rotational speed range including the idling range of an internal combustion engine can be increased without enlarging the outer diameter of the alternator, and the mechanical reliability is not impaired by the increase.
To achieve the above object, the automotive alternator of the invention comprises: a stator core having a stator winding; front and rear brackets which hold the stator core from both sides; a rotor core which is attached to a rotation shaft that is rotatably mounted on the brackets, and which has a field winding; a one-way clutch which has a driving member and a driven member, the driven member being fixed to the rotation shaft; an overdrive planetary gear mechanism which has a sun gear, a planet gear, and an outer ring gear, the sun gear being fixed to the rotation shaft, one end of a support shaft of the planet gear being fixed to the driving member of the one-way clutch, the outer ring gear being rotatably supported; an input shaft to which another end of the support shaft of the planet gear of the overdrive planetary gear mechanism is fixed, and which receives a driving force from an internal combustion engine; and an electromagnetic brake which operates in response to energization to block rotation of the outer ring gear of the overdrive planetary gear mechanism.
Moreover, the alternator has a housing which is attached to the front bracket, and which covers an axial end portion of the rotation shaft, one end of the input shaft is supported by a bearing disposed on the housing, and another end of the input shaft is supported by the rotation shaft via the support shaft of the planet gear and the one-way clutch.
Furthermore, a bearing is disposed on an outer diameter of the driving member of the one-way clutch, one end of a cylindrical member having the outer ring gear of the overdrive planetary gear mechanism is supported by the bearing, and another end of the cylindrical member is supported by the bearing disposed on the housing.
Furthermore, the automotive alternator of the invention comprises: stator core having a stator winding; front and rear brackets which hold the stator core from both sides; a rotor core which is attached to a rotation shaft that is rotatably mounted on the brackets, and which has a field winding; an overdrive planetary gear mechanism which has a sun gear, a planet gear, and an outer ring gear, the sun gear being fixed to the rotation shaft, one end of a support shaft of the planet gear being fixed to the driving member of the one-way clutch, the outer ring gear being rotatably supported; an input shaft to which the support shaft of the planet gear of the overdrive planetary gear mechanism is fixed, and which receives a driving force from an internal combustion engine; a one-way clutch which has a driving member and a driven member, the driving member being fixed to the input shaft, the driven member being coupled with a member having the outer ring gear of the overdrive planetary gear mechanism; and an electromagnetic brake which operates in response to energization to block rotation of the outer ring gear of the overdrive planetary gear mechanism.
Moreover, the alternator has a housing which is attached to the front bracket, and which covers an axial end portion of the rotation shaft, one end of the input shaft is supported by a bearing disposed on the housing, via the one-way clutch, the alternator further has a support member which is elongated from another end of the input shaft, and the support member is supported by a bearing disposed on the front bracket.
Furthermore, the alternator has a housing which is attached to the front bracket, and which covers an axial end portion of the rotation shaft, one end of the input shaft is supported by a bearing disposed on the housing, via the one-way clutch, the alternator further has a support member which is elongated from another end of the input shaft, and the support member is supported by a bearing disposed on the rotation shaft.
Moreover, the automotive alternator of the invention comprises: a stator core having a stator winding; front and rear brackets which hold the stator core from both sides; a rotor core which is attached to a rotation shaft that is rotatably mounted on the brackets, and which has a field winding; a one-way clutch which has a driving member and a driven member, the driven member being fixed to the rotation shaft, the driving member being integrated with an input shaft driven by an internal combustion engine; an overdrive planetary gear mechanism which has a sun gear, a planet gear, and an outer ring gear, the sun gear being fixed to the rotation shaft, a support shaft of the planet gear being fixed to the driving member which is integrated with the input shaft, the outer ring gear being rotatably supported; and an electromagnetic brake which operates in response to energization to block rotation of the outer ring gear of the overdrive planetary gear mechanism.
Moreover, one end portion of a member having the outer ring gear is supported by the rotation shaft via a bearing, and another end of the member is supported via a bearing by an outer diameter of the driving member which is integrated with the input shaft.
Furthermore, the alternator has a housing which is attached to the front bracket, and which covers an axial end portion of the rotation shaft, and the driving member of the one-way clutch which is integrated with the input shaft is supported by a bearing disposed on the housing.
Moreover, the driving member of the one-way clutch is attached to the input shaft via an elastic member.
Furthermore, the input shaft which is driven by the internal combustion engine is configured to be separable from the driving member of the one-way clutch.
Moreover, the sun gear of the overdrive planetary gear mechanism which is fixed to the rotation shaft, and the driven member of the one-way clutch are integrally formed.
Furthermore, the sun gear of the overdrive planetary gear mechanism which is fixed to the rotation shaft, and the driven member of the one-way clutch are separably formed.
Moreover, bearings which rotatably support a member having the outer ring gear are disposed respectively in two places in an axial direction, and at least one of the bearings bears radial and axial loads.
Furthermore, the electromagnetic brake has: an exciting coil which magnetizes a magnetic path; and a moving element which is attracted by magnetization of the magnetic path to block rotation of the outer ring gear of the overdrive planetary gear mechanism, the electromagnetic brake is accommodated in the housing, and guide grooves which mutually engage with each other are formed in an inner face of the housing, and an outer face of the moving element.
Moreover, the member having the outer ring gear is formed into a U-like section shape having a bottom face and two side faces, the bottom face is a face abutting against the moving element of the electromagnetic brake, the two side faces surround inner and outer peripheries of the electromagnetic brake, and a gap between inner faces of the two side faces and an outer face of the magnetic path is larger as moving toward an opening of the U-like section shape.